The goals of the proposed research are to increase our understanding of the way in which the visual system processes information based on color differences and to investigate visual responses to patterns which contain both color and luminance variations. Experiments addressing the former will consist in part of psychophysical and electrophysiological studies of selectivity for patterns which vary only in chromaticity along different spatial dimensions such as spatial frequency and orientation. These will be compared to selectivity for similar isochromatic luminance-varying patterns. Other studies will attempt to relate threshold sensitivity to color differences to suprathreshold color perception involved and study the underlying cortical organization in both color-normal and color-deficient subjects. The proposed studies of color-luminance interactions will be of several kinds. Psychophysical masking experiments will examine the effect of luminance contrast on the detectability of various chromatic patterns, and vice versa. Contrast, spatial frequency and orientation of the various patterns will be systematically varied. In physiological experiments the sensitivity of single cortical cells to chromatic variations will be measured both alone and in the presence of luminance contrast. The converse will also be done.